DEM modelling to assess internal stability of gap-graded assemblies of spherical particles under various relative densities, fine contents and gap ratios

Abstract

It is believed that the relative density (Dr) can affect the internal stability of the gap-graded soils and hence the erosion of their fine particles (i.e. susceptibility to suffusion). This paper investigates the influence of Dr on the contribution of fine particles on soil fabric. A new procedure is proposed to produce samples with target Dr using the discrete element method (DEM). DEM simulations were carried out using spherical particles. Particulate scale analysis of variation of stress reduction factor (α DEM ), the evolution of contact type and fine particle coordination number (Z fine ) with Dr reveals how Dr affects packing stability. The results show that packings with a fine content of 35% and the gap ratio in a range of 4-7 are in the transitional zone in which they are unstable initially and become internally stable as Dr increases. The behaviour of gap graded soil in the transitional zone is governed by fine-coarse contacts, but fine-fine contacts dominate the behaviour when soil becomes internally stable. Both α DEM and Z fine are reliable parameters in determining internal stability of gap graded soils. Finally, the correlation between the results and macro-scale matrix phase diagrams confirms the validity of micro-scale information to describe the underlying phenomenon.

Use of DEM in geomechanics: Special issue associated with the DEM 8 conference

“…All papers were subject to the standard, rigorous peer review required for publication in Computers and Geotechnics, resulting in the final 10 papers in this special issue. The papers themselves can be classified into 4 categories: (i) Developments in the DEM method (Duriez and Bonelli (2021), Li, Zhang and Duan (2020) advance understanding of material behaviour ( (Otsubo et al, 2020), (Ahmadi et al, 2020), and (Huang et al, 2020)), (iii) Use of DEM to simulate problems involving coupled fluidparticle interactions (Hu et al, Li, Zhang and Duan (2020), Xu and Dong (2021), Yamashiro and Tomac ( 2021)) (iv) Application of DEM to boundary value problems (Pol andGabrielli (2021), , Zhang et al, (2021)). These categories broadly reflect our analyses of DEM papers in Computers and Geotechnics, however there is a clear interest in coupled CFD-DEM simulations in this special issue.…”

“…This paper along with the contribution by Li, Zhang and Duan (2020) From a geomechanics perspective, one motivation to use DEM that it enables us to study the origins of the complexity of the mechanical behaviour of soil in physical regimes ranging from quasi-static to dynamic. There are three examples of use of DEM in this way in this special issue: Ahmadi et al, (2020) focused on internal stability, Otsubo et al, (2020) analyzed wave propagation and Huang et al, (2020) considered liquefaction. Otsubo et al, (2020) investigated the anisotropy of small-strain stiffness by simulating elastic wave propagation in granular soils under a K0 stress-state; they considered particles with different aspect ratios and varied the particle major axis orientation.…”

“…Otsubo et al, (2020) highlighted the importance of selecting a sensible contact law when non-spherical particles are adopted. Ahmadi et al, (2020) presented a DEM study on the influence of relative density on the internal stability of gap graded soils. Based on their numerical study, they showed that for some cases, a gapgraded soil which is initially unstable can become internally stable by increasing the relative density.…”

“…It is interesting to note that only three of the papers use LIGGGHTS/LAMMPS which can be compiled to run on large distributed memory, high performance computers. However, the largest simulations documented in this special issue were carried out by Ahmadi et al, (2020) using the windows-based code PFC3D.…”

Mesoscale Investigation of Fine Grain Contribution to Contact Stress in Granular Materials

“…The mass proportion of fine grains (usually named fine content or simply FC) has a significant effect on the mechanical properties of grain assemblies, and the role of fine grains in mixtures has received an acute attention in the literature (Lade and Yamamuro 1997;Monkul and Ozden 2007;Papadopoulou and Tika 2008;Cabalar 2011;Jiang et al 2015;Zhou et al 2018;Rahman et al 2011;Shi et al 2019;Shi et al 2021;Thevanayagam et al 2002;Cao et al 2021;Ng et al 2017;Zhou et al 2018;Ueda et al 2011). From a numerical point of view, discrete element methods (DEM) stand as an interesting tool to access to detailed and extensive information at grain scale level and improve the understanding of the mechanical role of fine grains in granular materials (Ahmadi et al 2020;Gong and Liu 2017;Gong et al 2019a and2019b). For instance, DEM simulations showed that fine grains exhibit a smaller effective stress than coarse grains in gap-graded materials with low fine contents (Shire and O'Sullivan 2013;Shire et al 2014).…”